Preparation of cyclohexanone



United States Patent PREPARATION OF CYCLOHEXANONE Dario Cova, St. Louis, Mo., assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Filed Apr. 21, 1959, Ser. No. 807,763

Claims. (Cl. 260586) This invention relates to the preparation of cyclohexanone and more specifically pertains to the preparation of cyclohexanone by the catalytic dehydrogenation of cyclohexanol.

It is known that cyclohexanol can be dehydrogenated in the presence of a dehydrogenation catalyst to cyclohexanone in either the liquid or the vapor phase. Some preference has been shown for the vapor phase dehydrogenation for the reason that the liquid phase dehydrogenation slows down substantially after only a small amount of cyclohexanol has been converted to cyclohexanone.

It has now been discovered that dehydrogenation of cyclohexanol in the liquid phase to cyclohexanone can be readily accomplished by boiling cyclohexanol with a dehydrogenation catalyst, whereby there is formed a vaporous mixture of cyclohexanone and cyclohexanol, passing said vaporous mixture from the dehydrogenation zone into contact with water in a rectification zone, the quantity of water added to the rectification zone being less than the quantity required to form water azeotropes with all of the cyclohexanone and cyclohexanol leaving the upper portion of the rectification zone, and removing from the upper portion of the rectification zone a water, cyclohexanone and cyclohexanol fraction and from the lower portion of said zone a cyclohexanol fraction essentially free from water and cyclohexanone. The water, cyclohexanone and cyclohexanol fraction removed overhead contains a higher proportion of cyclohexanone than the vaporous mixture entering the rectification zone. The essentially pure cyclohexanol fraction leaving the rectification zone may be returned for further dehydrogenation either by returning this directly to the dehydrogenation zone or to a feed tank where it is mixed with fresh cyclohexan-ol.

As stated above, the quantity of water added to the rectification zone is less than the quantity required to form an azeotrope with the cyclohexanone and the cyclohexanol vapor leaving the upper portion of the rectification zone. This may be accomplished by controlling the addition of water, so that the vapor phase temperature (i.e. the head temperature) will always be above the azeotrope temperature. The head temperature is generally within the range from about 100 C. to about 145 C. at atmospheric pressure. This corresponds essentially to the condition wherein the amount of water added is less than the quantity required to form water azeotropes with the cyclohexanol and cyclohexanone leaving the upper portion of the rectification zone, but above about the quantity required to provide 0.1 part by weight of water per part by weight of the cyclohexanone and cyclohexanol leaving the upper portion of the rectification zone.

The water can be added at virtually any point in the rectification zone, e.g. the top, the middle or the lower portion, or at a multiplicity of points. Preferably, the water is separately introduced at a single point in the column. The point of water addition should be above the point at which appreciable quantities of water will be present in the cyclohexanol bottoms, i.e. the cyclo- Patented Jan. 31, 1961 "ice hexanol fraction defined heretofore as being essentially free from cyclohexanone and water.

In one embodiment of the present invention the water, cyclohexanone and cyclohexanol fraction leaving the upper portion of the rectification zone is condensed and a portion of this condensate is returned to the rectification zone as reflux, while the remaining portion is taken off as product. It is preferred to return a major portion of this condensate to the column as reflux, so that the reflux ratio (L/D) is greater than one.

In a more preferred embodiment the water, cyclohexanone and cyclohexanol fraction is condensed and then passed into a separator where there is formed an upper (lighter) organic phase and a lower (heavier) water phase. The upper organic phase is split into two portions; a major portion of the organic phase is returned to the rectification zone as reflux, while a minor portion of this organic phase is withdrawn as crude product. In this embodiment the water is added in the lower portion of the column, e.g. the lower one-half, and preferably in the lower one-third of the column. When operating in this manner it is preferred to control the water addition by adding a sufiicient quantity of water to maintain the temperature at the point of water addition (i.e. the vapor phase temperature) within the range of to 135 C. at atmospheric pressure. It is even more preferred to maintain this temperature at the higher end of this range, e.g. from to C. The lower water phase is preferably returned to the point of water addition, so that the only fresh water added is that required to replace the water dissolved in the crude cyclohexanone product. In this embodiment liquid cyclohexanol essentially free from water and cyclohexanone is returned directly to the dehydrogenation reactor.

As catalysts there are used catalysts which are known for dehydrogenation reactions, as for example the metals of the 5th to 8th groups of the periodic system of elements, as well as their oxides and sulfides. The catalysts may be used as such or after application to carriers, as for example pumice, silicic acid, silicates, bleaching earths, active alumina or bauxite. They may be rigidly arranged in the dehydrogenation zone, i.e. in the dehydrogenation reactor, or may be present in a moving state. Finely divided nickel is a preferred catalyst for such dehydrogenation reactor.

The above described process of this invention is applicable to both batch and continuous operation. It is especially useful in continuous operations where eflicient conversion of cyclohexanol to cyclohexanone and maintenance of the catalyst activity are prime considerations.

When carrying out the process according to the invention, any suitable apparatus may be used for eifecting the rectification of the vaporous mixture coming from the dehydrogenation zone. One common type involves a vertical column containing packing material, bubble plates or sieve plates.

The following specific examples are intended as illustrations of the process of this invention, and it is not desired or intended that they be a limitation thereon. Unless specified otherwise, the parts disclosed in the following examples are parts by weight.

EXAMPLE I 200 parts by weight of cyclohexanol and 3.1 parts by weight of finely divided nickel were heated to boiling (161 C.) and the vapors passed into a short pack column used as a rectification zone. As soon as rectification conditions are established in the rectification zone water is added to the rectification zone in an amount sufficient to form an azeotrope with cyclohexanone and cyclohexanol. This azeotrope has a boiling point of about 97 C. The foregoing conditions of operation are continued while about 87 parts by weight of cyclohexanol per hour are added to the boiling mixture. The amount of water added per hour is about 13 parts by weight. There is removed from the upper portion of the rectification zone a mixture of cyclohexanol and water containing about 44% by weight of cyclohexanone, 43% cyclohexanol and 13% by weight of water. The reflux returning from the rectification zone to the boiling mixture of cyclohexanol and nickel catalyst consisted essentially of cyclohexanol since the temperature of the boiling mixture did not drop.

EXAMPLE II The process of Example I is repeated except that cyclohexanol is added continuously at a rate of 87 parts by weight per hour to a boiling pool containing 700 parts by weight cyclohexanol and 14 parts by weight of finely divided nickel as soon as rectification and withdrawal of the water, cyclohexanol and cyclohexanone azeotropes is established. After 40 hours of operation of this dehydrogenation process the vapors being withdrawn from the upper portion of the rectification zone still contain about 44% cyclohexanone, 43% cyclohexanol and about 13% water and the amount of cyclohexanol and cyclohexanone being withdrawn are substantially equivalent to the amount of cyclohexanol being added to the boiling pool of cyclohexanol.

EXAMPLE III A mixture containing about 700 parts by weight of cyclohexanol and about 14 parts by weight of finely divided nickel is heated to boiling and the vapors therefrom passed into a rectification zone as described in Example I. Water is added continuously to the rectification zone as soon as rectification conditions are established and cyclohexanol is added continuously at the rate of 59 parts by weight per hour. There is withdrawn from the upper portion of the rectification zone a mixture of cyclohexanone, cyclohexanol and water containing about 61% cyclohexanone, 26% cyclohexanol and 13% water. The overhead portion removed fro-m the rectification zone remained the same even after many hours of operation.

EXAMPLE IV Into a suitable reactor there is charged 785 parts of cyclohexanol and 16 parts of fully divided nickel. The resulting mixture is then heated to 161 C. and the vaporous mixture is passed through a vapor line to the bottom of the rectification zone (a 1" column filled with 36" of glass helices). The vapors are taken off overhead and condensed and a portion of the overhead condensate is refluxed. As soon as rectification conditions are established, water is added to the top of the column in an amount which is suflicient to maintain the head temperature (i.e. the vapor phase temperature at the point of water addition) at about 105 C. The foregoing conditions of operation are continued while there is added to the boiling mixture about 114 parts of cyclohexanol per hour. The overhead is condensed and one-third of the condensate is returned to the column as reflux and the other two-thirds is collected. This latter portion is allowed to separate into two phases, an upper organic phase and a lower water phase. The lower water phase is returnd to a water feed tank. The upper organic phase is a mixture containing about 44% cyclohexanone, 43% cyclohexanol, and 13% water. The liquid returning from the bottom of the rectification zone to the boiling mixture of cyclohexanol and nickel catalyst consists essentially of cyclohexanol, since the temperature of the boiling mixture remains essentially constant. After forty hours of operation the organic phase of the distillate still contains about 44% cyclohexanone, 43% cyclohexanol and about 13% water. The entire process is carried. out at atmospheric pressure.

In contrast to this process, a continuous process is carried out under otherwise identical conditions. the one exception being that water is not added to the rectification zone. Initially there is withdrawn from the upper part of the rectification zone a mixture containing about 37% of cyclohexanone and the remainder cyclohexanol. However, after forty hours of operation the organic phase of the distillate contains about 23% of cyclohexanone, the remainder being cyclohexanol.

EXAMPLE V Into a suitable reactor there is charged 485 parts of cyclohexanol and 14 parts of finely divided nickel. The resulting mixture is heated to 161 C., and the vaporous mixture is passed through a vapor line to the bottom of the rectification zone (a 4;" diameter column filled with 36 of A" MacMahon packing). As soon as rectification conditions are established, water is added to the column at a point 12'' up from the bottom of the packing and in an amount which is suflicient to maintain the temperature at the point of water addition at about 110 C. This temperature was measured by inserting a thermocouple at this point so that the thermocouple registered the vapor phase temperature. The foregoing conditions of operation are continued while there is added about 70 parts of cyclohexanol per hour to the boiling mixture in the dehydrogenation zone (i.e. the dehydrogenation reactor). In this process the overhead from the rectification zone is condensed and the condensate is passed into a separator where it is allowed to separate into two layers, an upper organic phase and a lower water phase. The upper organic phase is split so that the reflux ratio (L/D) is 1.05 to 1. The lower water phase is returned to the point of water addition and the only fresh water added is that quantity which is necessary to make up for the water dissolved in the organic phase of the distillate which is removed from the system. Under steady state conditions the quantity of water added is about 3.4! parts per minute (this includes 3.4 parts of recycle water and 0.17 parts of fresh water). The liquid returning from the bottom of the rectification zone to the boiiing mixture of cyclohexanol and nickel catalyst consists essentially of cyclohexanol (about 10% or less cyclohexanone), since the temperature of the boiling mixture remains essentially constant. After about forty-seven hours of operation the organic phase from the distillate is analyzed and found to contain about 48% cyclohexanone, 40% cyclohexanol and 12% water. The percent conversion is 56.1%. This is obtained by dividing the percent assay (i.e. pounds crude product X assay) by 96.04 percent dissolved water) 98/l00]. The foregoing process is carried out at atmospheric pressure.

Tabulated in Table 1 below are the results of operation of the process described in Example V above carried out at different reflux ratios. different temperatures at the same point of water addition and for different lengths of time, but using the same feed rate, sojourn time, catalyst concentration and reactor temperature.

Table I CONTINUOUS DEHYDRA'IION 0F CYCLOHEXANOL IN THE LIQUID PHASE WITH WATER ADDED TO THE RECTIFICATION ZONE S toad y Tern Cyclo- Length State (Hat Reflux hoxanono Percent Example of Run Water Point of Rat-to Assay 01 Conn:- Number (hrs) Addition Water (L/D) Organic sion (parts per Addition Phase minute) (id'lhesa figures include about 0.17 part per minute of fresh water that is a e The efficiency of the cyclohexanone separation in the rectification zone is apparent from the data presented in the foregoing table. It is even more apparent that catalyst activity remains high over extended periods of time by operating according to the process of the invention, as evidenced by the high conversions obtained.

EXAMPLE X The process of Example I is repeated except that cyclohexanol is added continuously at a rate of 98 parts per hour to a boiling pool containing 800 parts of cyclohex anol and 24 parts of finely divided nickel. As soon as rectification conditions are established there is added to the top of the column an amount of water which is suflicient to maintain the head temperature at 134 C. The reflux ratio is 5:1 (L/D=5). The run is continued for 312 hours, during which time the dehydrogenation reactor temperature rises from 160' C. to 217 C. due to high boiler formation. At the beginning of the run of concentration of cyclohexanone in the organic phase of the distillate is 47% and towards the end of the run the cyclohexanone concentration of the distillate is 52%.

In the operation of rectification zone according to the process of this invention the liquid cyclohexanol fraction which is withdrawn from the bottom of the rectification zone will contain ordinarily less than about 12% of cyclohexanone.

While the processes of these foregoing examples are carried out at atmospheric pressure, low superatmospheric pressures (i.e. up to 50 p.s.i.g.) may be employed in some instances to insure a practical rate of reaction. Subatmospheric or high superatmospheric pressures may be employed, however, no distinct advantages ensue from such a method of operation. Therefore, this process is desirably carried out at pressure within the range of from atmospheric pressure up to low superatmospheric pressure.

It is preferred that the cyclohexanol use be essentially dry. For the purposes of this invention cyclohexanol containing dissolved water up to the limit of solubility is considered to be dry.

The foregoing illustrates the process of this invention and contrasts it with a dehydrogenation process wherein water is not contacted with the vapors from the dehydrogenation zone. The superior results and the advantages to be gained from the process of this invention will be ap parent to those skilled in the art.

While this invention has been described with respect to certain embodiments, it is not so limited. It is to be understood that variations and modifications thereof which are obvious to those skilled in the art may be made without departing from the spirit or scope of the invention.

This application is a continuation-in-part of US. application, Serial Number 599,344, filed July 23, 1956, now abandoned.

What is claimed is:

1. In a process for the preparation of cyclohexanone by the liquid phase catalytic dehydrogenation of cyclohexanol within a dehydrogenation zone, the steps comprising (l) removing from said dehydrogenation zone a vaporous mixture containing cyclohexanol and cyclohexanone, (2) passing said vaporous mixture into contact with water within a rectification zone, the quantity of water added to said zone being less than the quantity required to form water azeotropes with all of the cyclohexanone and cyclohexanol leaving the upper portion of said rectification zone, but above about the quantity required to provide 0.1 part by weight of water per part by weight of the cyclohexanol and cyclohexanone leaving the upper portion of the rectification zone. and (3) removing from said rectification zone a water, cyclohexanone and cyclohexanol fraction and a cyclohexanol fraction essentially free from water and cyclohexanone.

2. In a process for the preparation of cyclohexanone by the liquid phase catalytic dehydrogenation of cyclohexanol. the teps comprising (1) maintaining within a dehydrogenation zone. at about its boiling point. a liquid phase dehydrogenation reaction mixture comprising cyclohexanol and a dehydrogenation catalyst and forming a vaporous mixture of cyclohexanol and cyclohexanone, (2) removing said vaporous mixture of cyclohexanone and cyclohexanol from said dehydrogenation zone and passing these vapors into a rectification zone, (3) introducing into said rectification zone a quantity of water which is less than the quantity required to form azeotrop'es with the cyclohexano and cyclohexanone leaving the upper portion of the rectification zone but sufilcient to maintain the head temperature within the range corresponding to to 145 C. at atmospheric pressure, (4) removing from the upper portion of the rectification zone a vaporous mixture of water, cyclohexanone and cyclohexanol, (5) removing from the lower portion of said rectification zone liquid cyclohexanol essentially free from water and cyclohexanone.

3. The process of claim 2 in which the dehydrogenation and rectification is carried out at a pressure within the range of from about atmospheric pressure to about 50 p.s.i.g.

4. The process of claim 3 in which the dehydrogenation catalyst is finely divided nickel.

5. In a process for the preparation of cyclohexanone by the liquid phase, catalytic dehydrogenation of cyclohexanol the steps comprising (l) maintaining within a dehydrogenation zone, at about its boiling point, a liquid phase dehydrogenation reaction mixture comprising cyclohexanol and a dehydrogenation catalyst so as to form a vaporous mixture of cyclohexanol and cyclohexanone, (2) continuously removing said vaporous mixture of cyclohexanone and cyclohexanol from said dehydrogenation zone and passing these vapors into a rectification zone. (3) continuously introducing into the lower portion of said rectification zone a quantity of water which is sufficient to maintain the temperature at the point of water addition within the range of from about C. to about C. (4) continuously removing from the upper portion of said rectification zone a vaporous mixture of water, cyclohexanone and cyclohexanol, (5) continuously condensing said vaporous mixture to form a condensate (6) continuously returning a major portion of the condensate to the rectification zone as reflux, (7) continuously removing a minor portion of condensate as product, (8) continuously removing from the lower portion of said rectification zone liquid cyclohexanol essentially free from water and cyclohcxanone and, (9) continuously returning said liquid cyclohexanol to said dehydrogenation zone.

6. In a process for the preparation of cyclohexanone by the liquid phase catalytic dehydrogenation of cyclohexanol, the steps comprising (1) maintaining within a dehydrogenation zone, at about its boiling point, a liquid phase dehydrogenation reaction mixture comprising cyclohexanol and a dehydrogenation catalyst so as to form a vaporous mixture of cyclohexanol and cyclohexanone, (2) continuously removing said vaporous mixture of cyclohexanone and cyclohexanol from said dehydrogenation zone and passing these vapors into a rectification zone. (3) continuously introducing into the lower one-third of said rectification zone a quantity of water which is sufficient to maintain the temperature at the point of water addition within the range of from about 110 C. to about 135 C., (4) continuously removing from the upper portion of the rectification zone a vaporous mixture of water, cyclohexanone and cyclohexanol, (5) continuously condensing said vaporous mixture to form a two phase condensate having an organic phase and a water phase, (6) continuously removing a minor portion of the organic phase and continuously returning a major portion of the organic phase to the rectification zone as reflux, (7) continuously removing from the lower portion of said rectification zone liquid cyclohexanol essentially free from water and cyclohexanone, and (8) continuously returning said liquid cyclohexanol to said dehydrogenation zone.

7. The process of claim 6 in which the dehydrogenw at the point of water addition is maintained within the tion catalyst is finely divided nickel. range of from about 125 to about 135 C.

8. The process of claim 7 wherein the dehydrogenation and rectification is carried out at atmospheric pres- References Cited in the file of this patent sure. 5

9. The process of claim 8 in which the lower water UNITED STATES PATENTS phase of the distillate is returned directly to the point of 1,392,011 Sandkflhl C- 27, 1932 water additior 2,303,550 Houghlon et a1. Dec. 1,

10. The process of claim 8 in which the temperature 2, 7 R y Dec. 23, 1952 

1. IN A PROCESS FOR THE PREPARATION OF CYCLOHEXANONE BY THE LIQUID PHASE DEHYDROGENATION OF CYCLOHEXANOL WITHIN A DEHYDROGENATION ZONE, THE STEPS COMPRISING (1) REMOVING FROM SAID DEHYDROGENATION ZONE A VAPOROUS MIXTURE CONTAINING CYCLOHEXANOL AND CYCLOHEXANONE, (2) PASSING SAID VAPOROUS MIXTURE INTO CONTACT WITH WATER WITHIN A RECTIFICATION ZONE, THE QUANTITY OF WATER ADDED TO SAID ZONE BEING LESS THAN THE QUANTITY REQUIRED TO FORM WATER AZEOTROPES WITH ALL OF THE CYCLOHEXANONE AND CYCLOHEXANOL LEAVING THE UPPER PORTION OF SAID RECTIFICATION ZONE, BUT ABOVE ABOUT THE QUANTITY REQUIRED TO PROVIDE 0.1 PART BY WEIGHT OF WATER PER PART BY WEIGHT OF THE CYCLOHEXANOL AND CYCLOHEXANONE LEAVING THE UPPER PORTION OF THE RECTIFICATION ZONE, AND (3) REMOVING FROM SAID RECTIFICATION ZONE A WATER, CYCLOHEXANONE AND CYCLOHEXANOL FRACTION AND A CYCLOHEXANOL FRACTION ESSENTIALLY FREE FROM WATER AND CYCLOHEXANONE. 